The present invention relates to printing presses, e.g. a lithographic printing press having an ink fountain, and relates in particular to apparatus for displaying the performance of a printing press to an operator for purposes, for example, of adjusting the press. In the prior art, printing presses commonly have been made employing a plurality of ink rate adjustment devices, such as ink keys distributed laterally across the width of the press, to adjust the rate at which ink is supplied to various lateral portions of the rolls of the press, and therefore to the paper being printed. One such system displays simultaneously the settings of all of the ink control devices of a printing unit, with the settings displayed side by side in the same order as the ink control devices themselves are arranged across the width of the printing press, and with an interpolating dot at the end of each setting display when appropriate, but not in combination with a density deviation display as herein.
Printing presses have been equipped in the past with optical densitometers that measure the reflection density of printed areas on the paper to monitor the ink density. A densitometer of this type is disclosed in U.S. Pat. No. 3,756,725 issued Sept. 4, 1973, made a part hereof by reference, in which presettable reference levels are provided for automatic comparison with reflection density readings that are made by the densitometer. In still other equipment of the prior art, analog strip chart recorders have been connected with the printing presses to record traces of deviations of densitometer measurements from predetermined set points; these charts give the user a visual indication of a number of recent measurements of reflection density.